doing more think on the colosseum battle arena idea ... I was able to make a little restocking-after-delay ammo pickup system no too bad. the problem is that it's not at all like tf2 where you just pick up a crate and everyone can use it. there's like 15 different types of ammo.
maybe the solution to this is to just have secondary weapons that all use the same ammo (like 9mm) and if you run out of ammo for your primary ... tough shit